The present application relates to an optical device which defines an optical path of light emitted from a directional light source, a light irradiation apparatus having the optical device, and a light irradiation method.
In the field of directional light sources such as lasers and LEDs (Light Emission Diodes), it is requested to form desired light by selecting the spot shape, the spot size, the light amount, the energy profile and the like of directional light emitted from such a light source.
For example, laser light is widely used in various processes, such as laser repair, laser anneal, laser cleaning and laser etching, which are used in defect repair of photomasks for use in manufacture of semiconductor devices, liquid crystal displays or organic electroluminescence displays and are also used in wiring repair of TFT circuit boards. However, the quality of a laser beam is not always in the desirable state for processing when the laser beam is emitted from a light source. For example, if a large variation occurs in energy intensity in a plane of a laser beam, which is planar, i.e., orthogonal to the optical path thereof, the large variation causes processing nonuniformity (a variation in processing rate) in a processing target surface of a light irradiation target to be processed.
To cope with this disadvantage, the above-mentioned processes have heretofore employed laser light which is formed and irradiated with a reduced energy variation by passing only the section of a laser beam which does not contain a large energy variation in cross section through a slit or the like, or by enlarging the beam width through a lens or the like and reducing the energy variation, after having measured a planar energy intensity distribution, i.e., energy profile, of the laser beam. However, these methods produce large energy losses, because the energy of the beam section blocked by the slit is lost and because the energy density of the laser beam to be used in irradiation with an enlarged beam width is decreased.
On the other hand, it has been proposed to provide a method of reducing a variation in energy distribution in a laser beam by a technique such as the technique of averaging beam profiles while reflecting the laser beam by a multiplicity of times by using an optical element called a homogenizer (see, Japanese Patent Application Publication No. Hei8-338962, Japanese Patent Application Publication Hei11-352419, Japanese Patent Application Publication 2001-350117 and Japanese Patent Application Publication 2002-224877).
However, in general, a homogenizer needs a complicated construction and is made of a large number of parts, and causes an increase in the cost required to construct a light irradiation apparatus for laser processing, i.e., an optical system.
In the light irradiation apparatus, various optical elements, such as a mirror for introducing light to a processing target section which is a section in which an irradiation target is to be disposed, and a lens for reducing the diameter of a light spot, are provided on an optical path of directional light emitted from a directional light source such as a laser light oscillation source. However, if the structure of the homogenizer is complicated, when, for example, a variation in the status of a laser beam (such as a variation in the beam profile or a deviation of the optical axis) occurs due to any apparatus trouble, the entire optical mechanism of the light irradiation apparatus needs to be re-adjusted in accurate response to the variation. As a result, troubleshooting cannot be completed in a short time and recovery of the apparatus takes long time.
Furthermore, there may occur a variation in a beam status which is difficult to handle with only the adjustment of the optical system. In this case, the specifications of the homogenizer itself need to be modified or changed, but the homogenizer needs to be designed for each individual laser, for example, by measuring the profile of laser light, according to the construction of the directional light source constituting the light irradiation apparatus or the construction of the entire light irradiation apparatus. As a result, it is also difficult to presume a variation in the beam status and prepare a replacement homogenizer in advance. For this reason, it is particularly desired that the optical system of a light irradiation apparatus used at the point of production be made as simple as possible in construction.